Hydro energy potential of cooling water at the thermal power plant

The hydro energy of the gravity water flow from the coal-fired thermal power plant units to the river in an open cooling system of turbine condensers is determined. On the basis of statistical data for a long time period, the water net head duration curve due to the river annual level change, as well as the reduction of the hydro energy potential due to the thermal power plant overhauls periods, are evaluated in the case study of the Thermal Power Plant “Nikola Tesla B” in Serbia. A small hydro power plant is designed for the utilization of this hydro energy, and the economic benefits of the project are calculated. The internal rate of returns and pay back periods are calculated in dependence of the electricity price and total investment costs. The increase of profitability is assessed, bearing in mind that the plant might be realized as the Clean Development Mechanism project according to the Kyoto protocol. The obtained results show that the project is economically attractive, and it can be carried out with standard matured solutions of hydro turbines available at the market. Even for the relatively low electricity price from small hydro power plants in Serbia of 0.08 €/kW h the internal rate of return and the pay back period are 17.5% and 5.5 years.     

Wetting and Spreading Of Liquid Metals Through Open Microgrooves and Surface Alterations

Surface-tension-driven flows (isothermal or non-isothermal) of microlayers of complex liquids over substrates under reactive wetting conditions at elevated temperatures are greatly influenced by interface interactions and topography of surface alterations. For example, understanding of the spreading of molten metals over metal substrates with complex topography may be interpreted as spreading over multiple connected networks of open microchannels. Hence, understanding of the kinetics of wetting and spreading of such reactive systems through microchannels is of a key interest. This article provides an overview of wetting/spreading phenomena related to migration of molten metal microlayer over smooth, rough, and/or well-organized-topography surfaces, such as microchannels. Systems involving a liquid metal medium temperature range (at ～850–873 K, Al-Si over Al), and a low temperature range (～420–520 K, Pb-Sn and Ag-Sn over Cu and Cu-Sn) have been considered. Kinetics data involving triple-line movement and its modeling were supported by real-time in situ visualizations. Targeted applications of these fundamental studies involve the art of brazing of compact aluminum heat exchangers for HVAC&R (heating, ventilation, air conditioning, and refrigeration), thermal management for aerospace, and soldering processes (in particular lead-free) for electronics industries.     

Analysis of Fin-Tube Joints in a Compact Heat Exchanger

This article deals with an analysis of fin-tube joints as functions of topological alterations of the joint fillet size. Based on numerical predictions of a joint topology formed by the surface tension driven reactive flow of molten metal, and subsequently verified by empirical evidence gathered through both laboratory and industrial testing, the topology alterations were identified for thermal integrity studies. Subsequently, thermal characteristics of corresponding fin-tube joints were determined in terms of two models of the thermal contact resistance. Model predictions of the fin efficiency with an altered topology of the joint zone were compared with the simulation results from a computational fluid dynamics study, and the results fit well. Numerical predictions of joint topology were devised using an in-house-developed finite-element code, and verified by the Surface Evolver code. Such prediction provided quantitative joint topology information that was needed in assessments of the joint thermal performance. Experimental data were obtained using a computer-controlled transparent hot zone with an ultra-high-purity nitrogen background atmosphere under tightly controlled conditions, and also by an analysis of the state-of-the-art manufacturing process data obtained from an industrial setting. It is demonstrated that a value of fin efficiency, assumed as recommended by traditional sizing design procedures, may drastically differ from actual values.     

Chemical functionalization of diatom silica microparticles for adsorption of gold (III) ions

Diatom silica microparticles from natural diatomaceous earth (DE) silica have been functionalized with 3-mercaptopropyltrimethoxysilane (MPTMS) and their application for adsorption of gold (III) ions from aqueous solutions is demonstrated. Fourier transform infrared spectroscopy (FTIR) and X-ray Photoelectron spectroscopy (XPS) analyses of the MPTMS modified diatom microparticles revealed that the silane layer with functional group (-SH) was successfully introduced to the diatom surface. The adsorption study of Au(III) ions using MPTMS-DE indicated that the process depends on initial gold (III) concentration and pH showing maximum adsorption capacity at pH = 3. The Au(III) adsorption kinetics results showed that the adsorption was very fast and followed a pseudo-second-order reaction model. The Langmuir model was used to provide a sound mechanistic basis for the theoretical of the adsorption equilibrium data. Gold recovery from MPTMS-DE structures was also investigated by using acidified thiourea solution and found to be high (> 95%). These results show that chemically modified DE microparticles can be used as a new, cost effective and environmentally benign adsorbent suitable for adsorption of gold metal ions from aqueous solutions.     

A nanoporous interferometric micro-sensor for biomedical detection of volatile sulphur compounds

ABSTRACT: This work presents the use of nanoporous anodic aluminium oxide [AAO] for reflective interferometric sensing of volatile sulphur compounds and hydrogen sulphide [H2S] gas. Detection is based on changes of the interference signal from AAO porous layer as a result of specific adsorption of gas molecules with sulphur functional groups on a gold-coated surface. A nanoporous AAO sensing platform with optimised pore diameters (30 nm) and length (4 μm) was fabricated using a two-step anodization process in 0.3 M oxalic, followed by coating with a thin gold film (8 nm). The AAO is assembled in a specially designed microfluidic chip supported with a miniature fibre optic system that is able to measure changes of reflective interference signal (Fabry-Perrot fringes). When the sensor is exposed to a small concentration of H2S gas, the interference signal showed a concentration-dependent wavelength shifting of the Fabry-Perot interference fringe spectrum, as a result of the adsorption of H2S molecules on the Au surface and changes in the refractive index of the AAO. A practical biomedical application of reflectometric interference spectroscopy [RIfS] Au-AAO sensor for malodour measurement was successfully shown. The RIfS method based on a nanoporous AAO platform is simple, easy to miniaturise, inexpensive and has great potential for development of gas sensing devices for a range of medical and environmental applications.     

Effect of preparation route on the microstructure and electrical conductivity of co-doped ceria

Dense Ce_0.8Sm_0.1Gd_0.1O_2?δ electrolytes were fabricated by sintering of CeO₂ solid solutions which were prepared from metal nitrates and NaOH using self propagating room temperature synthesis (SPRT). Three different routes were employed to obtain CeO₂ solid solution powders: (I) hand mixing of reactants, (II) ball milling of reactants and (III) ball milling of Ce_0.8Sm_0.2O_2?δ and Ce_0.8Gd_0.2O_2?δ solid solutions previously prepared by ball milling of corresponding nitrates and NaOH. Density measurements showed that ball milling, which is more convenient than hand mixing, is an effective way to obtain almost full dense samples after presureless sintering at 1550 °C for 1 h. These samples had larger grain size and consequently higher conductivity than the samples obtained by hand mixing. The highest conductivity of 2.704×10^?2 (Ω cm)^?1was measured at 700 °C in a sample prepared by route II. It was found that reduced grain size in samples obtained by hand mixing leads to a decrease in grain boundary conductivity and therefore decrease in the total conductivity. The results showed that mixing of single doped ceria solid solutions improved densification and inhibited grain growth.     

Outage analysis of selection diversity over Rayleigh fading channels with multiple co-channel interferers

In this paper an approach to the performance analysis of signal-to-interference (SIR) based selection combining (SC) operating over the Rayleigh fading channels experiencing an arbitrary number of multiple, Rayleigh co-channel interferers is presented. We have presented a general analysis of multibranch SC where each branch experiences an arbitrary number of multiple equal power co-channel interferers. Useful closed form expressions are derived for the probability density function (PDF) and cumulative distribution function (CDF) at the output of the combiner. Also an outage analysis is performed in order to show the effects of the number of multiple interferers, diversity order and input SIR unbalance to the system performances.     

Heating Cable Application in Solving Paraffin Deposition Problem in Tubing

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Effects of copper and Al2O3 particles on characteristics of Cu–Al2O3 composites

High-energy milling was used for production of Cu–Al₂O₃ composites. The inert gas-atomized prealloyed copper powder containing 2 wt.%Al and the mixture of the different sized electrolytic copper powders with 4 wt.% commercial Al₂O₃ powders served as starting materials. Milling of prealloyed copper powders promotes formation of nano-sized Al₂O₃ particles by internal oxidation with oxygen from air. Hot-pressed compacts of composites obtained from 5 and 20 h milled powders were additionally subjected to the high-temperature exposure in argon at 800 °C for 1 and 5 h. Characterization of processed material was performed by optical and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness, as well as density and electrical conductivity measurements. Due to nano-sized Al₂O₃ particles microhardness and thermal stability of composite processed from milled prealloyed powders are higher than corresponding properties of composites processed from the milled powder mixtures. The results were discussed in terms of the effects of different size of starting copper powders and Al₂O₃ particles on the structure, strengthening of copper matrix, thermal stability and electrical conductivity of Cu–Al₂O₃ composites.     

Occlusion and ion exchange in the molten (lithium chloride-potassium chloride-alkali metal chloride) salt + zeolite 4A system with alkali metal chlorides of sodium, rubidium, and cesium

Interaction between molten salts of the type LiCl-KCl-MeCl (Me = Na, Rb, Cs, x _MeCl = 0 to 0.5, x _KCl/x _LiCl = 0.69) and zeolite 4A have been studied at 823 K. The main interactions between these salts and zeolite are molten salt occlusion to form salt-loaded zeolite and ion exchange between the molten salt and salt-loaded zeolite. No chemical reaction has been observed. The extent of occlusion is a function of the concentration of MeCl in the zeolite and is equal to 11±1 Cl⁻ per zeolite unit cell, (AlSiO₄)₁₂, at infinite MeCl dilution. The ion-exchange mole fraction equilibrium constants (separation factors) with respect to Li are decreasing functions of concentration of MeCl in the zeolite. At infinite MeCl dilution, they are equal to 0.84, 0.87, and 2.31 for NaCl, RbCl, and CsCl, respectively, and increase in the order Na<Rb<Cs at identical MeCl concentrations. The standard ion-exchange chemical potentials are equal to −(0.0±0.5) kJ·mol⁻¹, −(0.4±0.3) kJ·mol⁻¹, and −(6.5±0.5) kJ·mol⁻¹ for Na⁻, Rb⁻¹, and Cs⁺, respectively.